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Crack Deflection (crack + deflection)
Selected AbstractsRelationship between Microstructure and Fracture Toughness of Toughened Silicon Carbide CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2001Sung-Gu Lee Different microstructures in SiC ceramics containing Al2O3, Y2O3, and CaO as sintering additives were prepared by hot-pressing and subsequent annealing. The microstructures obtained were analyzed by image analysis. Crack deflection was frequently observed as the toughening mechanism in samples having elongated ,-SiC grains with aspect ratio >4, length >2 ,m, and grain thickness (t) <3 ,m (defined as key grains 1). Crack bridging was the dominant toughening mechanism observed in samples having grains with thickness of 1 ,m < t < 3 ,m and length >2 ,m (key grains 2). The values of fracture toughness varied from 5.4 to 8.7 MPa·m1/2 with respect to microstructural characteristics, characterized by mean grain thickness, mean aspect ratio, and total volume fraction of key grains. The difference in fracture toughness was mainly attributed to the amount of key grains participating in the toughening processes. [source] Composite Zirconium Silicides Through an In Situ ProcessINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 1 2006Jérôme Canel Zirconium silicides are being investigated for use as neutron reflector materials for the next generation of nuclear power devices. Hot isostatically pressed monolithic Zr3Si2 and reactive sintered ZrXSiY composite are currently under development. The composite is obtained in situ and contains a ZrSi matrix embedding shell-like Zr, Zr2Si, and ZrSi2 domains with volume ratios depending on the initial Zr/Si ratio. Despite the lack of information on the mechanical properties of zirconium silicides, the composite structure is assumed to have enhanced fracture toughness; conditions to improve it further are discussed on the basis of microstructural observations of crack deflection. [source] Study of epoxy toughened by in situ formed rubber nanoparticlesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008Jun Ma Abstract The effect of rubber nanoparticles on mechanical properties and fracture toughness was investigated. Rubber nanoparticles of 2,3 nm were in situ synthesized in epoxy taking advantage of the reaction of an oligomer diamine with epoxy. The chemical reaction was verified by gel permeation chromatography (GPC) and 1HNMR, and the microstructure was characterized by transmission electron microscope. The rubber nanoparticles caused much less Young's modulus deterioration but toughened epoxy to a similar degree in comparison with their peer liquid rubber that formed microscale particles during curing. Fifteen wt % of rubber nanoparticles increased fracture energy from 140 to 840 J/m2 with Young's modulus loss from 2.85 to 2.49 GPa. The toughening mechanism might be the stress relaxation of the matrix epoxy leading to larger plastic work absorbed at the crack tip; there is no particle cavitation or deformation; neither crack deflection nor particle bridging were observed. The compound containing rubber nanoparticles demonstrates Newtonian liquid behavior with increasing shear rate; it shows lower initial viscosity at low shear rate than neat epoxy; this provides supplementary evidence to NMR and GPC result. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Thermal Stability of a Chemically Vapor Deposited Multilayer Coating Containing Amorphous Silica and Rutile Titania on Hi-Nicalon FiberJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2003Jinil Lee A multilayer coating consisting of consecutive layers of amorphous-silica, rutile-titania, and amorphous-silica was prepared on Hi-Nicalon fiber by chemical vapor deposition at 1050°C. It appeared that the silica and titania layers were strongly bonded to each other with no evidence of detachment and crack deflection at the interface region. The layered structure became morphologically unstable because of the growth of titania grains, the crystallization of the silica layers, and the oxidation of the fiber on exposure to 1200°C in air for 92 h. [source] Control of Composition and Structure in Laminated Silicon Nitride/Boron Nitride CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2002Chang-an Wang Based on a biomimetic design, Si3N4/BN composites with laminated structures have been prepared and investigated through composition control and structure design. To further improve the mechanical properties of the composites, Si3N4 matrix layers were reinforced by SiC whiskers and BN separating layers were modified by adding Si3N4 or Al2O3. The results showed that the addition of SiC whiskers in the Si3N4 matrix layers could greatly improve the apparent fracture toughness (reaching 28.1 MPa·m1/2), at the same time keeping the higher bending strength (reaching 651.5 MPa) of the composites. Additions of 50 wt% Al2O3 or 10 wt% Si3N4 to BN interfacial layers had a beneficial effect on the strength and toughness of the laminated Si3N4/BN composites. Through observation of microstructure by SEM, multilevel toughening mechanisms contributing to high toughness of the laminated Si3N4/BN composites were present as the first-level toughening mechanisms from BN interfacial layers as crack deflection, bifurcation, and pull-out of matrix sheets, and the secondary toughening mechanism from whiskers in matrix layers. [source] Design and Fracture of Layered Al2O3/TZ3Y Composites Produced by Electrophoretic DepositionJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2001Benjamin Hatton Alumina/yttria-stablized tetragonal zirconia (Al2O3/TZ3Y) multilayer composites with strong interfaces and containing residual stresses were produced by electrophoretic deposition. As-synthesized and Vickers-indented samples with different layering designs have been tested in bending (up to 1300°C) to experimentally define conditions for crack deflection and flaw tolerance. The compressive residual stress in the Al2O3 layers (,r) is a function of layer thickness (t). It was found that the parameter ,r2t is an effective indicator of the fracture behavior, as predicted by strain energy release calculations. With decreasing ,r2t, the fracture followed a sequence from spontaneous delamination, multistage fracture with extensive crack deflection, to catastrophic failure with, and finally without, deflection steps. Decrease of ,r with increasing test temperature causes changes in fracture behavior which correspond to the room-temperature transitions of ,r2t. [source] Modeling the Ultimate Tensile Strength of Unidirectional Glass-Matrix CompositesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2000R. E. Dutton The ultimate tensile strengths of a unidirectional glass-matrix composite were measured as a function of fiber volume fraction. The results were compared with predictions, using a refined solution of the stress field generated by an axisymmetric damage model, which incorporated the effect of stress concentration in the fiber caused by the presence of a matrix crack both before and after deflection at the fiber/matrix interface. Two possible locations for the fiber failure were considered: (1) at a transverse matrix crack, near a bonded fiber/coating interface and (2) at the tip of a debond, at the fiber/coating interface. At low fiber volume fractions, the measured ultimate tensile strength matched the prediction calculated, assuming no crack deflection. For higher volume fractions, the predictions calculated for a debonded crack matched the observed values. The model results were relatively insensitive to debond length and interfacial shear stress for the range of values in this study. In comparison, the global load-sharing model, which does not account for the stress singularity at the fiber/matrix interface, was found to overpredict the values of the ultimate tensile strength for all fiber volume fractions. An important contribution of the present work was to introduce the use of fiber volume fraction as a parameter for testing theoretical predictions of the mode of fiber failure. [source] Cure kinetics, phase behaviors, and fracture properties of bismaleimide resin toughened by poly(phthalazinone ether ketone)POLYMER ENGINEERING & SCIENCE, Issue 12 2009Yongjin Han Poly(phthalazinone ether ketone)s (PPEK) were used to toughen bismaleimide (BMI) resin composed of 4,4,-bismaleimidodiphenyl methane (BMDM) and O,O, -diallyl bisphenyl A (DABPA). Dynamic differential scanning calorimetry (DSC) of the blends was carried out for kinetic analysis of the curing reaction. The reaction activation energy indicated that the reaction mechanism remained the same even after the incorporation of PPEK. The reaction-induced phase separation process in BMI/PPEK blends was investigated by optical microscopy (OM). The primary phase structure of the blends was fixed at the early stage of phase separation, and a secondary phase separation was observed as a result of the high viscosity of the blends. Scanning electron microscope (SEM) graphs showed that the morphology of the cured resin changed from a dispersed structure to a phase-inverted structure with the increase of PPEK content. Compared with the neat resin, the fracture toughness of the modified resin exhibits a moderate increase when PPEK was incorporated. Several toughening mechanisms, such as local plastic deformation, crack deflection, and branches, presumably took part in improving the toughness of BMI/PPEK blends on the basis of the morphology. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source] | ||||||||||||||||||||||